THE NATURE AND PROPAGATION OF LIGHT

OPTICS

• A branch of physics that deals with the behavior of light and other electromagnetic waves.

DISPERSION

• The separation of visible light into its different colors.

Line of Sight

“In order to view an object, you must sight along a line at that object; and when you do light will come from that object to your eye along the line of sight.”

Law of Reflection

“Once a normal to the surface at the point of incidence is drawn, the angle of incidence can then be determined. The light ray will then reflect in such a manner that the angle of incidence is equal to the angle of reflection.”

Law of Reflection

өi = өr

Where: өi = angle of incidence өr = angle of reflection

• The Law of Reflection is always observed regardless of the orientation of the object.

• Rough surfaces also reflect light.

Specular Reflection

• Reflection off of smooth surfaces such as mirrors or a calm body of water

Diffuse Reflection

• Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway

Application:

• Night Driving

Application:

• Photography

WHY IS AN IMAGE FORMED?

• An image is formed because light emanates from an object in a variety of directions. Some of this light (which we represent by rays) reaches the mirror and reflects off the mirror according to the law of reflection.

Image Location

• is the location in space where all the reflected light appears to diverge from.

• In the case of plane mirrors, the image is said to be a virtual image.

Characteristics of Plane Mirrors

1. The image formed is VIRTUAL2. Left-Right Reversal3. Relationship between the object’s distance

from the mirror and the image’s distance to the mirror. (They are equal)

4. The dimensions of the object is the same as the dimensions of the image.

• The image has the same dimensions as the object and is the same distance behind the mirror as the object is in front of the mirror.

REFLECTION AND REFRACTION

Law of Reflection and Refraction

• If λ0 is the wavelength in a vacuum, the same wave has shorter wavelength λ in a medium with index of refraction n.

TOTAL INTERNAL REFLECTION

• Under certain circumstances, all of the light could be reflected back from the interface even though the material is transparent.

• The angle of incidence for which the angle of refraction is 90 degrees is called the critical angle.

Where na > nb

Sample Problem

• Solve for the critical angle for a glass-air surface with n= 1.52 for glass.

SEATWORK½ c.w. DO NOT COPY THE QUESTIONS (SHOW COMPLETE SOLUTION)

1. Light travels from air into a material at an angle of incidence of 59°. If the angle of refraction is 41°, what is the index of refraction of the material?

2. Solve for the critical angle for water (nb = 1.33) on glass (na = 1.52).

3. Light goes from benzene (n = 1.50) into diamond (n = 2.42). If the angle of incidence is 60 degrees, what is the angle of refraction?